What is a purpose of an SSH host key?

What is a purpose of an SSH host key?

A.
It is the root key by which all user SSH keys must be signed.

B.
It authenticates any user that logs into a remote machine from the key’s host.

C.
It provides the server’s identity information to connecting SSH clients.

D.
It must be sent by any SSH client in addition to a user key in order to identify the client’s host.

E.
It is used by system services like cron, syslog or a backup job to automatically connect to remote hosts.

Explanation: